Some missing details, which I would call critical.
1) The day before there was a big AMA where players and developers talked about the story design, initiated and organized by the game studio. The fired developer was a prominent figure in the discussions, and the twitter thread was seen by most as an further extension to that AMA. People can have different opinion about this, but its important to know the context of when the twitter thread appeared.
2) The initial response by the community at large was both on reddit and on the official Guild Wars 2 Forum to not fire anyone. It was only later unearthed that the developer had also celebrated when cancer victim John Bane died at age 33. At this point many have pointed out that the community changed view and could no longer support having such individual in the community, and a massive thread called something like "Developers should also have to follow Anet own conduct policy" was created.
Hedging is useful, but there is some lines which companies and communities are unlikely to accept. Celebrating the death of cancer victims is one, and is likely not something any one want to be associated with. The second aspect is to not responding to art criticism with labeling the person as sexist to 10k followers, which given the close connection to Anet organized AMA and the fact that their name is directly next to the message could make Anet legal liable for slander. Third, game developer is closely connected to community management and there is a good reason why conduct policies exist and get enforced. One could argue in defense that twitter is "personal" and out of the conduct policy scope, but that is very much up to discussion and it seems that the guild wars 2 community is generally in favor that such policy do cover developers talking about the game on social media, especially in connection to community events.